Membrane installation

The dead-end setup is by far the easiest apparatus both in construction and use. Reactor and separation unit can be combined and only one pump is needed to pump in the feed. A cross-flow setup, on the other hand, needs a separation unit next to the actual reactor and an additional pump to provide a rapid circulation across the membrane. The major disadvantage of the dead-end filtration is the possibility of concentration polarization, which is defined as an accumulation of retained material on the feed side of the membrane. This effect causes non-optimal membrane performance since losses through membrane defects, which are of course always present, will be amplified by a high surface concentration. In extreme cases concentration polarization can also lead to precipitation of material and membrane fouling. A membrane installed in a cross-flow setup, preferably applied with a turbulent flow, will suffer much less from this... 

The use of membranes for this separation provides the EDC producer with an additional degree of freedom. Higher oxygen contents can be accepted in the cell gas. The cost of a membrane installation can be offset by the cost of upgrading or replacing electrolysers or by the capital and operating cost of providing many connections for additions of acid to the brine. 

In the Persian Gulf and North African areas (where oil activity is combined with a notable lack of fresh water), the first significant electric membrane installations were erected about five years ago, and as of April 1, 1960, more than 25 plants with an aggregate capacity of some 200,000 gallons per day were in operation or under construction to serve over 250,000 people with fresh drinking and culinary water in Saudi Arabia, Bahrain, Kuwait, Qatar, Egypt, Libya, Tunisia, and Algeria. 

Some of the largest plants for seawater desalination, wastewater treatment and gas separation are already based on membrane engineering. For example, the Ashkelon Desalination Plant for seawater reverse osmosis (SWRO), in Israel, has been fully operational since December 2005 and produces more than 100 million m3 of desalinated water per year. One of the largest submerged membrane bioreactor unit in the world was recently built in Porto Marghera (Italy) to treat tertiary water. The growth in membrane installations for water treatment in the past decade has resulted in a decreased cost of desalination facilities, with the consequence that the cost of the reclaimed water for membrane plants has also been reduced. 

High flow rates across the membrane surface help reduce the accumulation of solutes rejected by the membrane (referred to as concentration polarization) and impurities lodged on the membrane surface (i.e. fouling ). (See Section lbii.) Tubular membranes and flat-sheet membranes installed in thin channel plate-and-frame... 

Cleaning chemicals and lost product 10-100/m membrane installed-year... 

Membrane installations operated in nuclear industry are pressure-driven systems majority of them are reverse osmosis plants. Uncontrolled growth of operation pressure may result in module damage and valves leaks resulted in contamination hazard. The selection of appropriate pumps and security devices can avoid the danger of pressure overgrowth and its detrimental implications. The security valves outlets have to be connected with existing waste distribution systems to direct the eventual leaks to the waste collecting tanks. 

AU the tanks connected with membrane installation have to be equipped with tank level meters with devices and blockades of the pumps secured against overflow. Special collectors in the floor for contaminated solutions in case of unexpected overflow have to be designed. 

Membrane installations generate secondary wastes that have to be taken into consideration before plant design. Reverse osmosis produces permeate, which can be discharged after radioactivity control, and retentate that can undergo further processing. Usually the retentate is not suitable for solidification and further volume reduction is necessary. 

The RO process was implemented at the Institute of Atomic Energy, Swierk. The wastes collected there, from all users of nuclear materials in Poland, have to be processed before safe disposal. Until 1990 the wastes were treated by chemical methods that sometimes did not ensure sufficient decontamination. To reach the discharge standards the system of radioactive waste treatment was modernized. A new evaporator integrated with membrane installation replaced old technology based on chemical precipitation with sorption on inorganic sorbents. Two installations, EV and 3RO, can operate simultaneously or separately. The membrane plant is applied for initial concentration of the waste before the evaporator. It may be also used for final cleaning of the distillate, depending on actual needs. The need for additional distillate purification is necessitated due to entrainment of radionuclides with droplets or with the volatile radioactive compounds, which are carried over. 

Liquid radioactive waste was directed from the waste storage tank to the 8 m feed reservoir. After pretreatment with PP depth filters and injection of antisealant, the wastes were directed to the first stage of RO. The retentate from this stage was concentrated in the third RO unit. The concentrated solution could be directly solidified if the concentration of the total solute was appropriate (<250 g/dm ). The salt concentration is limited by the conditions of concrete solidification. If the concentration was not sufficient, the further concentration took place in the evaporator. Permeate from the first and third stages was directed to the permeate reservoir before the second RO unit. The product from the membrane installation (permeate from the second stage) was of required radiochemical purity and after the control of specific activity and salinity was discharged to the communal sewage. 

Need of pretreatment of the streams before membrane installations. 

Testing the influence of process conditions on stability and lifetime of particular membrane installation elements— the influence of salts that cause scaling (Na2S04, Na2C03, NaHCOa, Ca3(P04)2), the influence of radiation on membrane material... 

Reported Existing Membrane Installations Excluding Coating Color Recovery Installations in the Pulp and Paper Industry. The Filters from Burg Plant, Uetersen n ... 

Membrane Installations Using Norit Tubular Membranes... 

As we know, large surface areas are required for industrial applications of membrane processes. A practical solution for providing this large surface area is packing the membranes into a small unit called a module, as shown in Fig. 2. The module is the base for membrane installation and process design. 

In a typical example [20] 6.4 m of 0.2 pm membranes are used in a pilot scale operation, yielding average fluxes between 100 and 1251/m h in a installation working at 55°C. The concentration factor for the membrane installation varies between 6 and 12. Due to the extreme fouling nature of the feed, periodic cleaning is compulsory, but can be restricted to once a week. The system has been in operation since August 1992. The pay-back time is less than 3 years. 

A number of hydrocarbon separations have been intensely studied and piloted in recent years and commercialization is expected soon. Pervaporation is expected to be one of a number of proven options for sulfur and benzene removal from fuels and olefin/ paraffin separations. These plants will use robust, specially engineered polymer membranes, installed in large-scale tubular modules. 

Membrane installation, capacity of 1 mVh pure permeate, was composed of three stages of RO (Figure 25.3) preceded by pretreatment with polypropylene (PP) depth filters. The first two stages were used for purification, the third one for final concentration. Two types of spiral-wound reverse osmosis (SWRO) modules were used in the installation SU-720R and SU-810 (TORAY). Both types of modules worked under a pressure of 20 bar and with high salt... 

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